1. Field
The disclosed technology relates to a display device and a driving method thereof.
2. Description of the Related Technology
Flat panel display apparatuses include a liquid crystal display (LCD), a field emission display, a plasma display panel (PDP), an organic light emitting display device, and the like.
Among the flat panel display apparatuses, the organic light emitting display device displays an image by using an organic light emitting diode which generates light in response to the recombination of electrons and holes. The organic light emitting display device has a rapid response speed and is driven by low power consumption, and has excellent emission efficiency, luminance, and viewing angle, and thus receives attraction.
Generally, the organic light emitting display device is classified as either a passive matrix organic light emitting display device (PMOLED) or an active matrix organic light emitting display device (AMOLED) according to a driving mode of the organic light emitting diode.
The passive matrix type uses a driving mode in which a positive electrode and a negative electrode are formed to be perpendicular to each other and a negative electrode line and a positive electrode line are selectively driven, and the active matrix type is a driving mode in which a thin film transistor and a capacitor are integrated in each pixel to maintain voltage by capacitance. The passive matrix type has a simple structure and is cheap, but it is difficult to implement a large-sized or high-precision panel. In contrast, the active matrix type may be implemented as a large-sized or high-precision panel, but there are problems in that the control method thereof is technically difficult and costs are relatively high.
From the viewpoint of resolution, contrast, and operation speed, the active matrix organic light emitting display device (AMOLED) in which light is selectively emitted for each unit pixel has become mainstream. In one pixel of the active matrix OLED (hereinafter, referred to as an organic light emitting display device), the emission degree of the organic light emitting diode is controlled by controlling a driving transistor which supplies a driving current according to data voltage to the organic light emitting diode.
A difference in threshold voltage and current mobility among a plurality of driving transistors may occur in a display panel of the organic light emitting display device. The difference may occur according to a characteristic of poly-silicon, and manufacturing process, method, and environment of the driving transistor. In addition, the difference may occur due to deterioration of the driving transistor over time of use of the organic light emitting display device.
Although the same data voltage is applied to each pixel circuit, the outputted emission degree or luminosity of the pixel varies due to a nonuniform threshold voltage characteristic of the driving transistor. Accordingly, a spot phenomenon such as relatively dark particles occurs on a bright screen. That is, when the threshold voltages of the driving transistors are not uniform, although the same data voltage is applied, effective gate-source voltage Vgs output of the driving transistor which is directly associated with a driving current supplied to the organic light emitting diode varies. Accordingly, an accurate gray is not expressed according to a data signal and a spot occurs, and as a result, display quality is low.
A technology of compensating an image through compensation of threshold voltage distribution of the driving transistor has been developed, but recently, as a display panel is large-sized and thus a high-speed driving mode is required, it is difficult to sufficiently compensate threshold voltage for all pixels of the display panel.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.